ИЗУЧЕНИЕ СТРУКТУРНЫХ И РАЗМЕРНЫХ СВОЙСТВ СПИННИНГОВАННЫХ ПОРОШКОВ p–Bi0,5Sb1,5Te3, СКОМПАКТИРОВАННЫХ ГОРЯЧИМ ВАКУУМНЫМ ПРЕССОВАНИЕМ И ИСКРОВЫМ ПЛАЗМЕННЫМ СПЕКАНИЕМ

P–type thermoelectric Bi0,5Sb1,5Te3 powders were obtained by the melt spinning technique (extremely rapid quenching from the liquid state) and their structural and dimensional characteristics were characterized. The crystallographic group and the lattice parameters of the powders correspond to those for Bi0,5Sb1,5Te3 crystallized in equilibrium conditions which suggests the identity of the crystal structure. The powders were compacted by vacuum hot pressing and spark plasma sintering. We found that the partial axial texture [001] directed along the axis of pressure application could be formed during the compacting of the powders. Temperature dependences of the thermoelectric characteristics of the compacted material were measured in a direction perpendicular to the pressure application axis in the 100—700 K range. It is demonstrated that the compacted samples possess low thermal conductivity while retaining the Seebeck coefficient and the electrical conductivity values comparable to crystallized material; therefore ZT reaches 1,05—1,15 in the 330—350 K range which indicates high prospects of applying these technologies. Получены порошки термоэлектрического материала Bi0,5Sb1,5Te3 p−типа проводимости методом спиннингования расплава (сверхбыстрой закалки из жидкого состояния). Определены их структурные и размерные характеристики. Установленная кристаллографическая группа и параметры решетки порошкового материала соответствуют материалу p−Bi0,5Sb1,5Te3, закристаллизованному в равновесных условиях, что свидетельствует об идентичности их кристаллической структуры. Из порошков методами горячего вакуумного прессования и искрового плазменного спекания скомпактированы образцы. Установлено, что при компактировании спиннингованных порошков p−Bi0,5Sb1,5Te3 возможно возникновение частичной аксиальной текстуры [001], направленной вдоль оси приложения давления. Электрофизические и термоэлектрические свойства образцов измерены в направлении, перпендикулярном к оси приложения давления, в диапазоне температур 100—700 К. Показано, что образцы, приготовленные указанными методами, обладают низкой теплопроводностью, сохраняя при этом значения электропроводности и коэффициента Зеебека, сравнимые с аналогичными величинами для традиционных закристаллизованных материалов. За счет этого термоэлектрическая эффективность ZТ достигает значений 1,05—1,15 при 330— 350 К, что говорит о высокой перспективности применения указанных технологий.

First Results from the AMoRE-Pilot neutrinoless double beta decay experiment

The Advanced Molybdenum-based Rare process Experiment (AMoRE) aims to search for neutrinoless double beta decay (0$\nu\beta\beta$) of $^{100}$Mo with $\sim$100 kg of $^{100}$Mo-enriched molybdenum embedded in cryogenic detectors with a dual heat and light readout. At the current, pilot stage of the AMoRE project we employ six calcium molybdate crystals with a total mass of 1.9 kg, produced from $^{48}$Ca-depleted calcium and $^{100}$Mo-enriched molybdenum ($^{48\textrm{depl}}$Ca$^{100}$MoO$_4$). The simultaneous detection of heat(phonon) and scintillation (photon) signals is realized with high resolution metallic magnetic calorimeter sensors that operate at milli-Kelvin temperatures. This stage of the project is carried out in the Yangyang underground laboratory at a depth of 700 m. We report first results from the AMoRE-Pilot $0\nu\beta\beta$ search with a 111 kg$\cdot$d live exposure of $^{48\textrm{depl}}$Ca$^{100}$MoO$_4$ crystals. No evidence for $0\nu\beta\beta$ decay of $^{100}$Mo is found, and a upper limit is set for the half-life of 0$\nu\beta\beta$ of $^{100}$Mo of $T^{0\nu}_{1/2} > 9.5\times10^{22}$ y at 90% C.L.. This limit corresponds to an effective Majorana neutrino mass limit in the range $\langle m_{\beta\beta}\rangle\le(1.2-2.1)$ eV

Data analysis of the internal background measurements of 40Ca100MoO4 scintillation crystals

The sensitivity of neutrinoless double beta (02) decay experiments is mainly dependent on the internal background of a detector which, in its turn, is defined by the purity of material and possibility for selection of background events. The AMoRE (Advanced Mo based Rare process Experiment) collaboration plans to use 40Ca100MoO4 scintillation crystals as a detector for search of 02 decay of 100Mo isotope. A purpose of this pa-per is further investigation of internal background of 40Ca100MoO4 scintillation elements with a low background setup at YangYang underground laboratory. We present new approaches for selection of background events from analyzing data and the latest updated values of background index of 40Ca100MoO4 crystals as a result of the new technique application

Study of structural and dimensional characteristics of the melt spun p-Bi0.5Sb1.5Te3 powders compacted by vacuum hot pressing and spark plasma sintering

P-type thermoelectric Bi0,5Sb1,5Te3 powders were obtained by the melt spinning technique (extremely rapid quenching from the liquid state) and their structural and dimensional characteristics were characterized. The crystallographic group and the lattice parameters of the powders correspond to those for Bi0,5Sb1,5Te3 crystallized in equilibrium conditions which suggests the identity of the crystal structure. The powders were compacted by vacuum hot pressing and spark plasma sintering. We found that the partial axial texture [001] directed along the axis of pressure application could be formed during the compacting of the powders. Temperature dependences of the thermoelectric characteristics of the compacted material were measured in a direction perpendicular to the pressure application axis in the 100–700 K range. It is demonstrated that the compacted samples possess low thermal conductivity while retaining the Seebeck coefficient and the electrical conductivity values comparable to crystallized material; therefore ZT reaches 1.05–1.15 in the 330–350 K range which indicates high prospects of applying these technologies

Application of the Monte-Carlo refractive index matching (MCRIM) technique to the determination of the absolute light yield of a calcium molybdate scintillator

The use of 40Ca100MoO in experimental searches for neutrinoless double beta decay (0νDBD) relies on knowledge of fundamental scintillation properties of the material. In this work we determine the absolute light yield of calcium molybdate using Monte-Carlo refractive index matching technique (MCRIM). The MCRIM technique is a combination of experiment and simulations that allows the absolute light yield of scintillators to be determined by taking into account effects of refraction, scattering and absorption in the material. The light collection efficiency of the scintillator-detector assembly was simulated using the ZEMAX ray-tracing software. By tuning the optical parameters of the scintillation crystal, a model was derived that gives good agreement with the experimental results. It is shown that the light collection efficiency of scintillators increases with transmittance and scattering due to an enhanced probability for photons to escape the crystal volume. Using MCRIM, the absolute light yield for the 40Ca100MoO4 scintillator was found to be 7.5±1.2 ph/keV at room temperature. Comparative measurements using a CaWO4 scintillator as a reference show good agreement with this result. In that way, the study demonstrated the potential of the MCRIM technique as a tool for quantitative characterization of scintillation materials. © 2013 IOP Publishing Ltd and Sissa Medialab srl